U.S. patent number 7,943,386 [Application Number 12/067,226] was granted by the patent office on 2011-05-17 for apparatus and method for determining the volume fractions of the phases in a suspension.
This patent grant is currently assigned to Albert-Ludwigs-Universitaet Freiburg. Invention is credited to Jens Ducree, Markus Grumann, Lutz Riegger, Roland Zengerle.
United States Patent |
7,943,386 |
Grumann , et al. |
May 17, 2011 |
Apparatus and method for determining the volume fractions of the
phases in a suspension
Abstract
An apparatus for determining the volume fractions of the phases
in a suspension includes a body, a channel structure, which is
formed in the body, and an inlet area and a blind channel, which is
fluidically connected to and capable of being filled via the same.
Furthermore, a drive for imparting the body with rotation, so that
phase separation of the suspension in the blind channel takes
place, is provided. The blind channel includes such a channel
cross-section and/or such wetting properties that, when filling
same via the inlet area, higher capillary forces act in a first
cross-sectional area than in a second cross-sectional area, so that
at first the first cross-sectional area fills in the direction from
the inlet area toward the blind end of the blind channel and then
the second cross-sectional area fills in the direction from the
blind end toward the inlet area.
Inventors: |
Grumann; Markus (Muehlhelm,
DE), Ducree; Jens (Freiburg, DE), Zengerle;
Roland (Waldkirch, DE), Riegger; Lutz (Freiburg,
DE) |
Assignee: |
Albert-Ludwigs-Universitaet
Freiburg (Freiburg, DE)
|
Family
ID: |
37622253 |
Appl.
No.: |
12/067,226 |
Filed: |
October 5, 2006 |
PCT
Filed: |
October 05, 2006 |
PCT No.: |
PCT/EP2006/009660 |
371(c)(1),(2),(4) Date: |
April 18, 2008 |
PCT
Pub. No.: |
WO2007/042207 |
PCT
Pub. Date: |
April 19, 2007 |
Prior Publication Data
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Document
Identifier |
Publication Date |
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US 20080280365 A1 |
Nov 13, 2008 |
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Foreign Application Priority Data
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Oct 7, 2005 [DE] |
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10 2005 048 236 |
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Current U.S.
Class: |
436/70; 436/45;
422/73; 436/43; 436/63; 422/64; 436/180; 436/174; 436/177; 422/533;
73/61.68; 422/527; 422/72 |
Current CPC
Class: |
B01L
3/502769 (20130101); B01L 3/502746 (20130101); B01L
3/502753 (20130101); B01L 2400/088 (20130101); B01L
2200/0684 (20130101); Y10T 436/11 (20150115); B01L
2400/0406 (20130101); B01L 2400/0409 (20130101); B01L
2200/0621 (20130101); B01L 2200/0642 (20130101); B01L
2300/161 (20130101); Y10T 436/25375 (20150115); B01L
2300/089 (20130101); B01L 2300/0803 (20130101); Y10T
436/111666 (20150115); Y10T 436/25 (20150115); B01L
2300/028 (20130101); Y10T 436/2575 (20150115) |
Current International
Class: |
G01N
33/86 (20060101); G01N 33/48 (20060101); G01N
1/18 (20060101) |
Field of
Search: |
;436/43,45,63,70,174,177,180 ;422/63,64,68.1,72,73,100,101,527,533
;73/61.65,61.68 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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103 25 110 |
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Jan 2005 |
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DE |
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0 392 475 |
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Oct 1990 |
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EP |
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8-220088 |
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Aug 1996 |
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JP |
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2004-340758 |
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Dec 2004 |
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JP |
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94/18557 |
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Aug 1994 |
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WO |
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98/39645 |
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Sep 1998 |
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WO |
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99/41147 |
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Aug 1999 |
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WO |
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00/53321 |
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Sep 2000 |
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WO |
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2004/061413 |
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Jul 2004 |
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WO |
|
Other References
Official communication issued in counterpart International
Application No. PCT/EP2006/009660, mailed on May 8, 2008. cited by
other .
Official communication issued in the International Application No.
PCT/EP2006/009660 mailed on Jan. 30, 2007. cited by other .
Thomas, "Labor und Diagnose", pp. 492-495. cited by other .
Dorner: "Klinische Chemie und Hamatologie," Georg Thieme Verlag;
Germany; 1998; pp. 152-153. cited by other .
Goldschmidtboeing et al.: "Strategies for Void-Free Liquid-Filling
of Micro Cavitites," Proceedings of Transducers '05 Conference;
Jun. 5-9, 2005; pp. 1561-1564. cited by other .
Steinert et al.: "Bubble-Free Priming of Blind Channels,"
Proceedings of IEEE-MEMS; Jan. 25-29, 2004; pp. 224-228. cited by
other .
Kohnle et al.: "A Unique Solution for Preventing Clogging of Flow
Channels by Gas Bubbles," Technical Digest IEEE Micro Electro
Mechanical Systems; Jan. 22-24, 2002; p. 77-80. cited by other
.
Official Communication issued in corresponding Japanese Patent
Application No. 2008-533941, mailed on Sep. 7, 2010. cited by
other.
|
Primary Examiner: Wallenhorst; Maureen M
Attorney, Agent or Firm: Keating & Bennett, LLP
Claims
The invention claimed is:
1. An apparatus for determining the volume fractions of the phases
in a suspension, comprising: a body; a channel structure, which is
formed in the body and comprises an inlet area and a blind channel,
which is fluidically connected to and capable of being filled via
the inlet area; a drive for imparting the body with rotation, so
that phase separation of the suspension in the blind channel takes
place by centrifugation; and a controller to control the drive,
wherein the blind channel comprises such a channel cross-section
and/or such wetting properties that, when filling same with the
suspension via the inlet area, higher capillary forces act in a
first cross-sectional area than in a second cross-sectional area,
so that at first the first cross-sectional area fills in the
direction from the inlet area toward a blind end of the blind
channel by capillary force and then the second cross-sectional area
fills in the direction from the blind end toward the inlet area by
capillary force, the channel structure further comprises an
overflow structure between the inlet area and the blind channel for
volume dosage of the suspension, wherein the overflow structure
comprises an overflow channel branching from the blind channel and
extending in a partially radial direction to an overflow chamber,
and the controller is configured to control the drive such that,
upon completely filling the blind channel with the suspension by
capillary force, the body is imparted with a rotational frequency
that exceeds a breakthrough frequency of the overflow channel so
that excess suspension is drawn off into the overflow chamber and a
defined volume of the suspension is in the blind channel so that
phase separation of the suspension in the blind channel takes place
in the defined volume.
2. The apparatus according to claim 1, wherein the body comprises a
scale, which is arranged relative to the blind channel such that
the volume fraction in the blind channel can be read.
3. The apparatus according to claim 1, wherein the body comprises a
first layer, in which the channel structure is formed, and a second
layer, which forms a lid.
4. The apparatus according to claim 1, wherein the body is formed
as a rotation body with a rotation axis, wherein the drive is
formed to rotate the rotation body about its rotation axis.
5. The apparatus according to claim 1, wherein the drive comprises
a fixture for holding the body and for rotating the body about a
rotation axis lying outside the body.
6. The apparatus according to claim 1, wherein the blind channel
comprises walls bordering on each other with different angles
enclosed therebetween.
7. The apparatus according to claim 1, wherein the blind channel
comprises walls, which are differently hydrophilic with respect to
the suspension or which comprise portions being differently
hydrophilic with respect to the suspension.
8. The apparatus according to claim 1, wherein the blind channel
comprises a cross-section with at least one step.
9. The apparatus according to claim 1, wherein the blind channel
comprises a T-shaped channel geometry.
10. The apparatus according to claim 1, wherein the blind channel
comprises an upper wall and a lower wall and at least one sidewall
arranged at an angle different from 90.degree. with respect to the
upper wall and the lower wall.
11. The apparatus according to claim 1, further comprising a
determinator for determining the volume fractions in the blind
channel during or after the rotation.
12. A method for determining the volume fractions of the phases in
a suspension, comprising: providing a channel structure, which
comprises an inlet area, a blind channel which borders on the inlet
area, and an overflow structure between the inlet area and the
blind channel for volume dosage of the suspension, wherein the
overflow structure comprises an overflow channel branching from the
blind channel and extending in a partially radial direction to an
overflow chamber; introducing the suspension into the inlet area,
wherein the blind channel comprises such a channel cross-section
and/or such wetting properties that higher capillary forces act in
a first cross-sectional area than in a second cross-sectional area,
so that at first the first cross-sectional area fills in the
direction from the inlet area toward a blind end of the blind
channel by capillary force and then the second cross-sectional area
fills in the direction from the blind end toward the inlet area by
capillary force; upon completely filling the blind channel with the
suspension by capillary force, imparting a rotational frequency to
the channel structure that exceeds a breakthrough frequency of the
overflow channel so that excess suspension is drawn off into the
overflow chamber and a defined volume of the suspension is in the
blind channel; imparting the channel structure with rotation, to
cause phase separation of the defined volume of the suspension in
the blind channel by centrifugation; and determining the volume
fractions of the separated phases in the blind channel.
13. The method according to claim 12, wherein the channel structure
is imparted with rotation prior to complete filling of the blind
channel by capillary force, in order to accelerate the filling by
taking advantage of centrifugal force.
14. The method according to claim 12, wherein the suspension is
blood and wherein the dimensions of the channel structure are
adapted to determine the hematocrit of blood.
15. The method according to claim 12, further comprising
determining the volume fractions in the blind channel during or
after the rotation.
Description
TECHNICAL FIELD
The present application relates to an apparatus and a method for
determining the volume fractions of the phases in a suspension,
i.e. a multi-phase mixture containing a liquid phase and a solid
phase. In particular, the present invention is suited for
determining the hematocrit value HKT of whole blood, i.e. the ratio
of the partial volume of the cellular constituents to the overall
volume.
BACKGROUND
Methods for determining the hematocrit value HKT of blood are
known. One known method for determining the hematocrit value is
based on an electrical conductance measurement, wherein the
measured conductance is inversely proportional to the hematocrit.
Such methods are described, for example, in "Labor und Diagnose" by
Lothar Thomas, TH-Books, 5.sup.th volume, 1998, and K. Dorner,
"Klinische Chemie und Hamatologie", Georg Thieme Verlag, Stuttgart,
Germany, 1998, 2003. Moreover, products for hematocrit
determination using electrical conductance measurement were offered
by iSTAT Corporation, East Windsor, N.J., USA
(http://www.istat.com) at the time of application.
A further method for determining the hematocrit value is referred
to as micro-hematocrit method. Here, a micro-capillary having an
internal diameter of 1 mm is dipped into the blood to be measured.
The blood rises in the capillary, driven by the capillary force.
This is now sealed at one end and inserted into a micro-hematocrit
centrifuge or a microhematocrit rotor, and centrifuged according to
the NCCLS standard. The determination of the hematocrit value HKT
takes place either by a measurement disk or a measurement assembly.
Direct readout of the hematocrit value is possible still in the
centrifuge with the measurement disk. The great disadvantage of
this method is the necessary manual sealing of the capillary.
The micro-hematocrit method is approved as a reference method,
wherein the values obtained are up to about 2% higher than the
comparative measurements with a hematology analyzer, due to the
enclosed plasma. With respect to this micro-hematocrit method, for
example, reference may be made to K. Dorner, Klinische Chemie und
Hamatologie, Georg Thieme Verlag, Stuttgart, Germany, 1998, 2003,
or B. Bull et al., Pennsylvania, USA, ISBN 1-56238-413-9 (1994).
Furthermore, this technology is practiced by the company Hermle
Labortechnik GmbH at the time of application
(http://www.hermle-labortechnik.de).
Methods for filling blind channels, i.e. channels with one closed
end, which are supposed to prevent enclosure of bubbles, are known.
Such methods are described, for example, in Steinert C P Sandmeier
H, Daub M., de Heij B., Zengerle R. (2004), Bubble free priming of
blind channels, in Proceedings of IEEE-MEMS, Jan. 25-29, 2004,
Maastricht, The Netherlands, p. 224-228; and Goldschmidtboeing F.,
Woias P. (2005), Strategies for Void-free Liquid-filling of Micro
Cavities, in Proceedings of Transducers '05 Conference, June 5-9,
Seoul, Korea, ISBN 07-7803-8994-8, p. 1561-1564; as well as in DE
10325110 B3.
SUMMARY
According to an embodiment, an apparatus for determining the volume
fractions of the phases in a suspension may have: a body; a channel
structure, which is formed in the body and has an inlet area and a
blind channel, which is fluidically connected to and capable of
being filled via the inlet area; and a drive for imparting the body
with rotation, so that phase separation of the suspension in the
blind channel takes place by centrifugation, wherein the blind
channel has such a channel cross-section and/or such wetting
properties that, when filling same with the suspension via the
inlet area, higher capillary forces act in a first cross-sectional
area than in a second cross-sectional area, so that at first the
first cross-sectional area fills in the direction from the inlet
area toward the blind end of the blind channel and then the second
cross-sectional area fills in the direction from the blind end
toward the inlet area.
According to another embodiment, a method for determining the
volume fractions of the phases in a suspension may have the steps
of: providing a channel structure, which has an inlet area and a
blind channel, which borders on the inlet area; introducing the
suspension into the inlet area, wherein the blind channel has such
a channel cross-section and/or such wetting properties that higher
capillary forces act in a first cross-sectional area than in a
second cross-sectional area, so that at first the first
cross-sectional area fills in the direction from the inlet area
toward the blind end and then the second cross-sectional area fills
in the direction from the blind end toward the inlet area; and
imparting the channel structure with rotation, to cause phase
separation of the suspension in the blind channel by
centrifugation.
The present invention relates to a novel concept to determine the
volume fractions of the phases in a multi-phase mixture. The
inventive concept here uses the effect of sedimentation in a blind
channel if the same is subjected to centrifugation. The blind
channel, according to the invention, includes such a channel
cross-section and/or such wetting properties that an asymmetric
capillary force occurs along the walls of the blind channel, which
results in capillary filling of the channel advantageously in the
area of the high capillary forces. Thereby, air is displaced into
the area of the low capillary force, and furthermore in the
direction of the inlet. Thus, by a quick filling rate in the area
of the high capillary forces, the associated cross-sectional area
of the channel is quickly filled in the direction from the open
side toward the closed side, whereupon the areas with the low
capillary force are filled in the direction from the blind end
toward the inlet. This allows for filling the blind channel
substantially without air enclosure. The blind channel thus can be
filled with the sample with defined and usually infinitesimal
bubble enclosure due to the channel cross-section and/or the
wetting properties. The blind channel is subjected to
centrifugation, so that phase separation of the suspension takes
place and the particles are sedimented out of the suspension.
In embodiments, the channel structure may comprise an integrated
overflow structure between inlet and blind channel for integrated
volume definition of the sample. In further embodiments, a scale
for reading the volume fractions may be integrated in the body in
which the channel structure is formed. The body in which the
channel structure is formed may be formed, in embodiments of the
present invention, by a first layer, in which the channel structure
is formed, and a second layer, which forms a lid.
So as to cause asymmetric capillary forces along the walls of the
blind channel, the blind channel may comprise walls bordering on
each other at different enclosed angles. Additionally or
alternatively, the walls may be differently hydrophilic with
respect to the suspension or comprise portions being differently
hydrophilic with respect to the suspension. Again alternatively or
additionally, the blind channel may comprise a cross-section with
at least one step, so that a capillary force distribution having
areas with higher capillary force and areas with lower capillary
force results across the cross-section of the blind channel.
In the inventive method for determining the volume fractions of the
phases in a suspension, the centrifugal force may further be used
to effect accelerated filling of the blind channel. To this end,
rotation of the channel structure may already be caused before the
blind channel is completely filled.
The present invention allows for complete integration of all
procedural steps necessary for hematocrit value determination,
particularly with no later sealing of a capillary being necessary.
Furthermore, the inventive apparatus may be produced via a simple
process, since the body may simply consist of two layers, with the
channel structure being structured in one thereof, whereas the
other serves as a lid. Alternatively, both layers may be structured
to define parts of the channel structure.
The present invention may be implemented as a so-called
"lab-on-a-disk" system, wherein further medical tests may be
integrated on the body, also taking advantage of centrifugal and
capillary forces as well as further forces usual in so-called
lab-on-a-chip systems. The present invention is particularly suited
for determining the hematocrit value of blood, wherein the
dimensions of the channel structure are adapted correspondingly, to
be able to effect sedimentation of the blood into erythrocytes and
plasma in the blind channel. Lab-on-a-chip systems are described,
for example, in A. van den Berg, E. Oosterbroek, Amsterdam, NL,
ISBN 0-444-51100-8 (2003).
The blind channel is designed for capillary filling with the
suspension the volume fractions of which are to be determined,
wherein filling thus may take place without centrifugal force. The
centrifugal force may, however, be used supportively to accelerate
the filling process by imparting the channel structure with
rotation during filling.
BRIEF DESCRIPTION OF THE DRAWINGS
Embodiments of the present invention will be detailed subsequently
referring to the appended drawings, in which:
FIG. 1 is a schematic illustration of a substrate according to an
embodiment of the invention;
FIG. 2 is a schematic cross-sectional illustration of a channel for
explaining an asymmetric capillary pressure distribution;
FIGS. 3A to 3F schematically show channel cross-sections, as may be
used in embodiments of the invention;
FIGS. 4A and 4B schematically show a respective portion of a
channel cross-section for explaining the generation of an
asymmetric channel pressure using different wetting angles;
FIG. 5 is a schematic perspective view of the blind end of an
embodiment of a blind channel the cross-section of which is shown
in FIG. 3A;
FIGS. 6A to 6C are side views of the channel shown in FIG. 5 in
different phases of the filling thereof;
FIGS. 6D to 6F are top views of the channel of FIG. 5, also in
different phases of filling thereof, corresponding to the phases of
FIGS. 6A to 6C;
FIGS. 7A to 7C show a channel structure at different times of an
embodiment of the inventive method;
FIG. 8 is a frequency protocol for control of a drive means during
the execution of an embodiment of the inventive method;
FIG. 9 schematically shows the result of a measurement series for
hematocrit determination using a channel structure, as it is shown
in FIG. 7;
FIGS. 10A and 10B are schematic top views of embodiments of a
substrate formed as a disk; and
FIG. 11 is a schematic side view of an embodiment of an inventive
apparatus.
DETAILED DESCRIPTION
The present invention is generally suited for determining the
volume fractions of the phases in a multi-phase mixture, and is
particularly applicable in advantageous manner for determining the
hematocrit value of blood.
Substantially, the present invention includes a body and a drive
means for imparting the body with rotation. The body may for
example comprise a lidded substrate, in which channel structures
are implemented, and may be set to rotation via a rotation motor.
Here, the body may either itself be formed as a rotation body, for
example a disk, which is placed onto a suitable coupling of the
rotation motor, or the body may be formed as a module insertable
into a rotor, which can be driven by a rotation motor. What is
important for technical realization rather is the balance of the
rotor than the exact shape of the body.
FIG. 1 shows a schematic top view onto an excerpt 10 of a
substrate, which may for example be implemented as a disk 12, as it
is shown in FIG. 10A. The substrate 12 may be constructed according
to a conventional CD type, having a center opening 14, by means of
which it may for example be attached at a conventional centrifuge.
An alternative embodiment of a substrate 12', in which a plurality
of channel structures are formed, which hence has a plurality of
areas 10, is shown in FIG. 10B. By the substrate shown in FIG. 10B,
in which five channel structures are formed, the hematocrit value
of five blood samples can be determined concurrently or also
successively.
As can be taken from FIG. 11, the substrate 12, in which the
channel structures are formed, are provided with a lid 16. The
substrate 12 and the lid 16 form a module body 18. The module body
18 is attached via a mounting means 20 to a rotating part 22 of a
driving device, which is pivoted on a stationary part 24 of the
driving device. The driving device may for example be a
conventional centrifuge with adjustable rotational speed or also a
CD or DVD drive. The driving device 24 includes a control means 26
to cause the respective rotations of the substrate 12 to perform
the method according to the invention.
As shown in FIG. 1, a channel structure in the substrate comprises
an inlet area 30 for the medium to be examined, which borders on a
blind channel. The substrate 12 is rotatable about a rotation axis
Z, so that the inlet area terminates radially outwardly into the
blind channel 32. In the inlet area, for example, there is a hole
34 in the lid of the substrate, as indicated by dashed lines in
FIG. 1. A sample may be introduced into the inlet area through the
hole.
The channel structure includes, in the example shown, also an
overflow structure 36, which comprises an overflow channel 38 and
an overflow chamber 40, into which the overflow channel 38 leads.
The overflow structure 36 serves for volume dosage of the sample,
i.e. of the suspension. The overflow channel 38 of the overflow
structure may represent a hydrophobic barrier for the dosage, which
is overcome after the filling of the blind channel 32, so that a
defined volume of the suspension is in the blind channel 32.
In the embodiment shown, the substrate 12 further includes a scale
42, which may for example be formed on or in the lid or on the
upper side of the carrier layer 16. The scale 42 allows for direct
optical readout of the volume of the phase fraction following the
sedimentation.
The blind channel 32 is formed such that different capillary forces
act in different cross-sectional areas thereof. In particular, the
blind channel may be formed to obtain differently strong capillary
forces along the edges of the channel. To this end, an angle of
inclination of the sidewalls of the channel with respect to a
perpendicular to the main surfaces of the substrate and/or the
contact angle of the inner channel wall with the suspension to be
sedimented can be adapted. In particular, zones with increased
capillary pressure may be generated thereby, wherein the expansion
of the menisci at the greatest speed then is along the zones with
the increased capillary pressure.
According to a first alternative, as it is schematically shown in
FIG. 2, the walls of the blind channel and/or the walls of the
entire channel structure (inlet and blind channel) may be inclined
by an angle .alpha.. By such an inclination .alpha., a differently
high capillary pressure at edges k1 and k2 of the channel results,
wherein a sidewall 46 and an upper wall 44 border on each other
with a smaller enclosed angle at the edge k1 than the sidewall 46
with a channel bottom wall 48 at the edge k2. Thus, there is a
higher capillary force in the area of the edge k1 than in the area
of the edge k2. The area adjacent to the edge k1 thus represents an
area of a higher capillary force, at which propagation of the
meniscus of a suspension with which the channel is to be filled
takes place at increased speed. Thus, it can be achieved that
filling at first takes place in these areas in the direction from
the inlet area toward the blind end, and the remaining areas then
fill in the direction from the blind end toward the inlet area.
Variations of channel cross-sections are shown in FIGS. 3A-3F,
wherein the channel each is formed in the substrate 12, which is
provided with a lid 16. In FIGS. 3A-3C, T channel cross-sections
are shown, the sidewalls of which exhibit increasingly greater
angles of inclination from FIG. 3A to 3C. An increased angle of
inclination .alpha. of one and/or more channel walls increases the
asymmetry of the capillary pressure.
In FIGS. 3D-3F, trapezoidal channel cross-sections are shown, the
sidewalls of which have increasingly higher angles of inclination
from FIG. 3D-3F, and hence increasingly higher asymmetry of the
capillary force.
The channel cross-sections shown in FIGS. 3A-3C here represent an
embodiment, since they allow for more reliable bubble-free filling.
The described cross-sections are advantageous in that they can be
produced in technically simple manner by usual milling tools.
Alternatively to the "oblique" T shapes shown in FIGS. 3A-3C, the
channel cross-section could also have a T shape with substantially
straight side faces, so that the channel has steps defining
cross-sectional areas in which there are different capillary
forces, so that substantially bubbly-free filling is possible
thereby.
As a further alternative, differently strong capillary pressures in
the channel edges can be realized by variation of the contact angle
.theta.. In this respect, FIG. 4A schematically shows an edge k3 of
a channel the channel walls of which are made hydrophilic with
respect to the suspension to be filled, such that a great contact
angle .theta. is present. Thereby, a high capillary force results
in the area of the edge k3. In contrast thereto, the channel walls
at the edge k4 shown in FIG. 4B are made hydrophilic with respect
to the suspension to be filled, such that a small contact angle
.theta. results. Thereby, there is a smaller contact angle in the
area of the edge k4.
According to FIGS. 4A and 4B, bubble-free filling of the
hydrophilic blind channel thus may also take place based on the
advantageous capillary filling along a certain part of the channel
wall by variation of the contact angle .theta., wherein the case
shown in FIG. 4A provides a capillary filling favored in comparison
with the case shown in FIG. 4B. An increased angle of inclination
.alpha. of the channel wall may additionally increase the asymmetry
of the capillary force. For example, it is possible to make the
inside of the lid 16 more strongly hydrophilic than the walls of
the substrate 12, so that a capillary force occurring on the edges
between the lid 16 and the substrate 12 is increased as opposed to
a capillary force occurring in an area on the edges between the
sidewalls and the channel bottom. Furthermore, wall sections of
individual walls may be made more strongly hydrophilic than others
so as to there create areas at which a higher capillary force
occurs than in other areas, so as to obtain the functionality
described.
In summary, it can be stated that the capillary force in different
cross-sectional areas of the blind channel is determined by the
geometrical angles and the wetting angles, so that the effect of
the blind channel at first being filled in the direction from the
open end toward the blind end in certain areas and the remaining
areas then being filled in the direction from the blind or closed
end toward the open end can be achieved by a corresponding
configuration of the channel cross-section using acute angles or
sufficient hydrophylization. In other words, filling with a fast
filling rate takes place in the areas with increased capillary
force, whereas filling with a slow filling rate takes place in the
areas with a low capillary force.
With respect to the theory of such a bubble-free filling capability
of blind channels and/or their design, reference is made to the
documents cited above, the disclosures of which in this respect are
incorporated by reference.
A perspective view of a channel structure having a channel
cross-section substantially corresponding to the cross-section
shown in FIG. 3A is shown in FIG. 5. The channel cross-section has
a T shape, the sidewalls of which have an angle of inclination
.alpha. of about 17.5.degree.. At the closed end 60 of the blind
channel, which is generally designated with the reference numeral
62, there is a transition area. In the channel structure shown in
FIG. 5, the outer areas of the crossbeam of the T structure, which
are schematically marked in FIG. 3A and designated with the
reference numeral 64, represent areas with increased capillary
pressure. Thus, filling takes place from the open side of the blind
channel 62 along these areas toward the closed end, as shown by an
arrow 66 in FIG. 5. At the closed end 60, there is provided a
transition so as to assist transition of the suspension into the
inner area not yet filled, which is designated with the reference
numeral 68 in FIG. 3A. This is indicated by an arrow 67 in FIG. 5.
Subsequently, the blind channel fills further in the direction from
the blind end 60 toward the open end, as indicated by an arrow 68
in FIG. 5.
In the case of a purely capillary filling, the transition area 62
is formed such that the capillary flow is not interrupted there. An
important measure to this end, for example, is the avoidance of
sharp transition edges. If this final phase of the capillary
filling is assisted by centrifugation, geometries that can be
filled not solely in capillary manner are also tolerable in the
area 62, without putting the overall functionality of the
blind-channel-based hematocrit determination at risk.
Channel structures, for example such as it is shown in FIG. 5, may
for example be produced using a CNC (computer numerically
controlled) micro-material treatment in a COC (cyclic olefin
copolymer) disk using a tapering tool, yielding walls having an
inclination of 17.5.degree.. The upper and the lower plane of the
two-plane capillary structure shown in FIG. 5 may for example have
a depth of 400 .mu.m, widths of 1400 .mu.m and 400 .mu.m,
respectively, and radial lengths of 25 mm and 25.4 mm,
respectively, with a transition at the closed end 60, as explained
above.
The inner channel walls are made hydrophilic with respect to the
suspension to be examined after producing the channel, due to the
substrate material used, or are made hydrophilic correspondingly
after producing the channel structures.
A sequence representing the filling of a blind channel, as it is
shown in FIGS. 3A and 5, is shown in FIGS. 6A-6F, wherein 6A-6C
show lateral longitudinal cross-sectional views, whereas FIGS.
6D-6F illustrate top views onto the channel structure shown in FIG.
5. The filling illustrated takes place without centrifugal force
assistance, wherein a time axis at the left edge of FIGS. 6A to 6C
indicates that the filling process up to the degree of filling
shown in FIGS. 6C and 6F takes about 30 seconds.
As can be seen in FIG. 6, the blind channel 62 is structured into a
substrate 70 and closed by means of a lid 72. As explained with
reference to FIGS. 4A and 5, the channel possesses areas 64 in
which there is increased capillary force and areas 68 in which
there is lower capillary force.
Upon introducing a suspension into an inlet area (not shown in
FIGS. 6A-6F), which is fluidically connected to the blind channel
62 at the open end, the suspension is drawn along the critical
edges between the inclined sidewalls and the lid by the capillary
force, as shown by the suspension areas 74 in FIGS. 6A and 6D and
indicated by the arrow 76 in FIG. 6A. After filling the areas 64 in
the direction from the open end toward the closed end of the blind
channel 62, the special shape of the closed end assists a seamless
transition of the suspension into the area 68 along the edges, as
can be seen in FIGS. 6B and 6E. This transition into the area 68 is
further supported by the fact that the edges at the closed end of
the blind capillaries are rounded. Then, filling of the still
unfilled area 68 in the direction from the closed end 60 of the
blind channel 62 toward the open end thereof takes place. This
leads to complete evacuation of the channel, so that this has
substantially been filled completely by the suspension without
bubble inclusion.
Execution of an example of an inventive method using a channel
structure having a channel 62, as it was described above, is shown
in FIGS. 7A-7C. The channel structure includes the blind channel
62, an inlet area 80, as well as an overflow structure 82. The
channel structures mentioned may again be formed in a substrate and
covered by a lid, which may again comprise an opening 84 for
introducing a suspension into the inlet area 80, which may
represent an inlet reservoir.
In FIG. 7A, there is shown the state in which the blind channel 62
is completely filled with the suspension to be sedimented. After
this filling, the rotational frequency is increased over the
breakthrough frequency of an overflow channel 86 of the overflow
structure 82, which is made hydrophobic at the entry, so that the
excess suspension is drawn off into the overflow reservoir 88 via
the overflow channel 86. FIG. 7B shows the channel structure after
dosing off the excess suspension using the overflow structure 82.
The limiting frequency for the breakthrough may for example be 30
Hz, wherein the suspension volume in the blind capillary 62 may for
example be 20 .mu.l. Then, the substrate in which the channel
structure is formed is further subjected to rotation, for example
at 100 Hz for five minutes, so that the suspension in the blind
channel 62 is sedimented. FIG. 7C shows the channel structure after
sedimentation. The volume fraction of the deposited sediment and/or
the hematocrit value may then be determined at rest via the ratio
of the radial position of the liquid-solid interface and the known
length of the capillary. Advantageously, a scale 90 located on the
substrate may be used for reading the hematocrit value.
FIG. 8 shows a possible frequency protocol for operating the
driving device, for example the rotation motor. At the beginning,
the rotational frequency is increased to 100 Hz, for example,
wherein the centrifugal force generated hereby may assist the
filling process. After exceeding the limiting frequency of the
overflow structure, the excess suspension flows into the suspension
reservoir 88. So as to cause sedimentation of the suspension in the
blind channel, rotation at a substantially constant rotational
speed takes place, whereupon the rotation is terminated by breaking
over a certain time interval. After the standstill, the volume
fraction can be read using the scale by an operator or
automatically via an optical detection means.
FIG. 9 shows the result of a measurement series for determining the
hematocrit value, which was obtained using the above-described
apparatus and with the described method. The reference
determination here takes place with the aid of a micro-hematocrit
rotor Z 233 M-2 of the company Hermle Labortechnik in a centrifuge
by the same company.
FIG. 9 shows that a CV value of 2.1% and high linearity between the
inventively obtained hematocrit value and the reference
measurement, R.sup.2=0.999, was obtained in a determination time of
five to six minutes.
Hence, the present invention provides a novel concept suited for
determining a centrifuge-based hematocrit test in a blind
capillary. The test may be implemented by a frequency protocol on a
simple two-plane structure, which may easily be achieved using
inexpensive mass production, for example injection molding. The
test is very exact and necessitates a blood volume of only 20
.mu.l. Moreover, readout by visual inspection on a printed scale
eliminates the need for expensive detection equipment, wherein the
hematocrit test could in principle be run on a conventional CD
drive. So as to achieve rotational symmetry of the disk, it may
further be advantageous to implement parallelization of channels,
as it was explained above with reference to FIG. 10B, which is of
particularly advantage for routine blood separation.
In embodiments of the present invention, there may further be
provided a possibility to allow for readout during or after the
rotation. To this end, a suitable measurement instrument may be
provided. This may for example comprise a photo camera with short
aperture time or a stroboscopic camera, to detect the blind
channel, with an associated scale if necessary. The measurement
instrument may further comprise an evaluation means to evaluate the
captured images and determine the hematocrit value therefrom.
The substrate in which the channel structures are formed may be
formed of any suitable materials, for example plastics, silicon,
metal or the like. Furthermore, the substrate and the structures
formed therein may be produced by suitable manufacturing methods,
for example micro-structuring or injection molding techniques. The
lid of the inventive substrate may consist of a suitable,
advantageously transparent material, for example glass of pyrex
glass.
With reference to the embodiments, the body of substrate and lid
has been described as a rotation body with a rotation axis, wherein
the drive means is formed to rotate the rotation body about its
rotation axis. Alternatively, the body may have a substantially
arbitrary shape, wherein the drive means comprises a fixture for
holding the body and for rotating the substrate about a rotation
axis lying outside the substrate.
While this invention has been described in terms of several
embodiments, there are alterations, permutations, and equivalents
which fall within the scope of this invention. It should also be
noted that there are many alternative ways of implementing the
methods and compositions of the present invention. It is therefore
intended that the following appended claims be interpreted as
including all such alterations, permutations and equivalents as
fall within the true spirit and scope of the present invention.
* * * * *
References